The present invention relates to an X-ray CT apparatus or a technique for an X-ray CT image photographing or imaging method, which realize cardiac imaging or biological synchronous imaging based on low radiation exposure, high image quality and high-speed photography by an electrocardiographically-synchronized helical scan, variable-pitch helical scan or helical shuttle scan at a medical X-ray CT (Computed Tomography) apparatus.
In an X-ray CT apparatus using a multi-row X-ray detector or an X-ray CT apparatus using a two-dimensional X-ray area detector of a matrix structure typified by a flat panel, the photography of the heart has heretofore been performed by a helical scan electrocardiographically synchronized at a helical pitch made slow by a helical pitch 0.2 or so as shown in FIG. 16. As the technique of photographing or imaging such as a heart by the helical scan, a patent document 1 has been known.
The present imaging method involves a problem in terms of X-ray exposure because of the low helical pitch. Data acquisition in which one segment is defined as fan angles+180° is shown in FIG. 16. However, as in the case in which multi-segment image reconstruction is taken as shown in FIGS. 17 and 18 to adapt to various heartbeats, problems arise even in terms of image quality as in the case of the occurrence of artifacts due to displacements in X-ray projection data between respective segments, the occurrence of banding artifacts in the direction orthogonal to a z direction parallel to an xy plane at a three-dimensional display as shown in FIG. 20, and the like.
[Patent Document 1] Japanese Unexamined Patent Publication No. 2003-164446
Assuming that, for example, an X ray having a beam width of 40 mm is used and imaging is done at a helical pitch 0.2, an imaging area is moved 8 mm per one scan rotation. Therefore, there is a need to carry out imaging corresponding to 15 rotations of a gantry for the purpose of imaging or photographing a heart whose overall length is 12 cm or so. Radiation dose reduction is typically desirable and it is desirable to reduce any X-ray projection data that may be unused in the actual diagnosis exist in large quantities, as well as about an exposed dose equivalent to greater than or equal to 5 times as compared with a conventional scan (axial scan) which enables imaging of 40 mm minutes per rotation of gantry. On the other hand, since a z direction X-ray detector width is not yet sufficient in the normal conventional scan (axial scan), data acquisition per rotation is not capable of covering the whole heart.
Therefore, an object of the present invention is to provide an X-ray CT apparatus capable of realizing the photography or imaging of a heart at a low dosage and a high speed and with good image quality by a helical scan, variable pitch helical scan or helical shuttle scan of the X-ray CT apparatus having a multi-row X-ray detector or a two-dimensional X-ray area detector of matrix structure typified by a flat panel X-ray detector.